Electrolyte and electrochemical device comprising the same

ABSTRACT

The present application relates to an electrolyte, and an electrochemical device comprising the electrolyte. The electrolyte comprises a fluorinated cyclic carbonate and a multi-nitrilemulti-nitrile compound having an ether bond, wherein based on the total weight of the electrolyte, the weight percentage (C f ) of the fluorinated cyclic carbonate is greater than the weight percentage (C n ) of the multi-nitrilemulti-nitrile compound having an ether bond. The electrolyte of the present application can control the expansion of the electrochemical device, so that the electrochemical device has excellent cycle, storage and/or floating-charge performance.

The present application claims the benefit of priority from the ChinaPatent Application No. 201811106537.0, filed on 21 Sep. 2018, thedisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND 1. Field of the Invention

The present application relates to the technical field of energy storagetechnologies, and more specifically to an electrolyte and anelectrochemical device comprising the electrolyte, particularly alithium ion battery.

2. Description of the Related Art

With the rapid development of intelligent electronic products,increasingly higher requirements are imposed on the energy density ofelectrochemical devices. Developing a high-voltage electrochemicaldevice is one of the effective methods. However, at a high voltage, theoxidizability of the cathode material is increased, and the stability islowered, which causes the non-aqueous electrolyte to easily decompose onthe surface of the cathode or cause deterioration of the batterymaterial, resulting in a decrease in battery capacity. The phenomenon inwhich an electrochemical device is continuously charged after fullcharge such that the electrochemical device is in a state of high chargefor a long time is referred to as floating charge. The floating-chargeperformance of the electrochemical device directly affects itsreliability, for example, swelling, extra-thickness and capacityattenuation.

In order to solve the above problems, it is definitely necessary toprovide an electrochemical device having excellent cycle, storage,and/or floating-charge performance, which can be attained by providingan improved electrolyte.

SUMMARY

An embodiment of the present application provides an electrolyte and anelectrochemical device comprising the electrolyte, to solve at least oneof the problems existing in the related art to some extent. Theelectrolyte of the present application can control the expansion of theelectrochemical device, so that the electrochemical device has excellentcycle, storage and/or floating-charge performance.

In one embodiment, the present application provides an electrolyte,which comprises a fluorinated cyclic carbonate and a multi-nitrilecompound having an ether bond, where based on the total weight of theelectrolyte, the weight percentage (C_(f)) of the fluorinated cycliccarbonate is greater than the weight percentage (C_(n)) of themulti-nitrile compound having an ether bond.

According to the embodiment of the present application, based on thetotal weight of the electrolyte, C_(f) is about 0.1 wt %-about 10 wt %,and C_(n) is about 0.1 wt %-about 5 wt %.

According to the embodiment of the present application, themulti-nitrile compound having an ether bond is selected from a compoundrepresented by General Formula [1]:

where:

R₁, R₂, and R₃ each represent —(CH₂)_(a)—CN or—(CH₂)_(b)—O—(CH₂)_(c)—CN;

R₄ represents hydrogen, an alkyl group having 1-5 carbon atoms,—(CH₂)_(a)—CN, or —(CH₂)_(b)—O—(CH₂)_(c)—CN;

at least one of R₁, R₂, R₃, and R₄ is —(CH₂)_(b)—O—(CH₂)_(c)—CN; and

a, b and c are each independently an integer from 0 to 10.

According to the embodiment of the present application, themulti-nitrile compound having an ether bond is selected from at leastone of the group consisting of 1,2,3-tris(2-cyanoethoxy)propane,1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane,1,1,1-tris(cyanoethoxymethylene)propane,3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane,1,2,6-tris(cyanoethoxy)hexane, and 1,2,5-tris(cyanoethoxy)pentane.

According to the embodiment of the present application, themulti-nitrile compound having an ether bond further comprises Compound1A:

According to the embodiment of the present application, the fluorinatedcyclic carbonate is selected from the group consisting of a fluorinatedcyclic carbonate having an alkylene group with 2-6 carbon atoms.

According to the embodiment of the present application, the fluorinatedcyclic carbonate is selected from at least one of the group consistingof fluoroethylene carbonate, 4,4-difluoroethylene carbonate,4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate,4,5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylenecarbonate, 4,4-difluoro-5-methylethylene carbonate,4-(fluoromethyl)-ethylene carbonate, 4-(difluoromethyl)-ethylenecarbonate, 4-(trifluoromethyl)-ethylene carbonate,4-(fluoromethyl)-4-fluoroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate,4,5-difluoro-4,5-dimethylethylene carbonate, and4,4-difluoro-5,5-dimethylethylene carbonate.

According to the embodiment of the present application, the electrolytefurther comprises a fluoroether selected from compounds of GeneralFormula [2], [3], [4] or [5]:Rf1-O—Rf2  [2],Rf1-O—R  [3],Rf1-O—(R′—O)_(n)—Rf2  [4],Rf1-O—(R′—O)_(n)—R  [5],

or a combination thereof,

where:

in Formulas [2], [3], [4], and [5], Rf1 and Rf2 are each independently alinear or branched C₁ to C₁₂ fluoroalkyl group having at least onehydrogen atom replaced by fluorine, R is a linear or branched C₁ to C₁₂alkyl group, and R′ is a linear or branched C₁ to C₅ alkylene group, andn is an integer from 1 to 5.

According to the embodiment of the present application, the electrolytefurther comprises a cyclic phosphonic anhydride, which is selected fromcompounds represented by General Formula [6]:

where:

R₅, R₆, and R₇ are each independently selected from hydrogen, an alkylgroup having 1-20 carbon atoms, and an aryl group having 6-26 carbonatoms; and

R₅, R₆ and R₇ are identical to or different from each other or any twoof them are identical.

According to the embodiment of the present application, the electrolytefurther comprises at least one of a cyclic carbonate having acarbon-carbon double bond, a fluorinated chain carbonate, a dinitrilecompound, and a compound having a sulfur-oxygen double bond.

According to the embodiment of the present application, the electrolytefurther comprises at least one of a cyclic carbonate, a chain carbonate,a cyclic carboxylate, a chain carboxylate, a cyclic ether, a chainether, a phosphorus-based organic solvent, a sulfur-containing organicsolvent, and an aromatic fluorine-containing solvent.

In another embodiment, the present application provides anelectrochemical device comprising an electrode and the electrolyte asdescribed above.

According to the embodiment of the present application, the electrolytecomprises at least one of ethyl propionate, propyl propionate, andγ-butyrolactone, which is present in a content of about 1 wt %-about 60wt % based on the total weight of the electrolyte.

According to an embodiment of the present application, the electrolytecomprises propyl propionate, which is present in a content of about 10wt %-about 50 wt % based on the total weight of the electrolyte.

According to the embodiment of the present application, the electrodecomprises a current collector and a coating that is at least oneselected from the group consisting of:

a single-sided coating formed by coating a slurry only on one surface ofthe current collector; and

a double-sided coating formed by coating a slurry on two opposingsurfaces of the current collector,

where the electrode including the single-sided coating has an electrodecompaction density D1, the electrode including the double-sided coatinghas an electrode compaction density D2, and D1 and D2 satisfy therelationship: about 0.8≤D1/D2≤about 1.2.

According to the embodiment of the present application, the electrodescomprise a cathode and an anode. In some embodiments, when the electrodeis a cathode, D2 meets the formula: about 3.5 g/cm³≤D2≤about 4.3 g/cm³.

In some other embodiments, when the electrode is an anode, D2 meets theformula: about 1.2 g/cm³≤D2≤1.8 g/cm³.

In another embodiment, the present application provides an electronicdevice including the electrochemical device as described above.

Additional aspects and advantages of the embodiments of the presentapplication will be partially described, illustrated or explained by wayof examples in the description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings needed for describing the embodiments of the presentapplication or the prior art will be briefly described below tofacilitate the description of the embodiments of the presentapplication. Obviously, the drawings in the following description onlyshow some embodiments of the present application. For those skilled inthe art, the drawings of other embodiments can be obtained according tothe structures illustrated in the drawings without creative efforts.

FIG. 1 is a view schematically showing the structure of an electrode Awith a single-sided coating according to an embodiment of the presentapplication.

FIG. 2 is a view schematically showing the structure of an electrode Bwith a double-sided coating according to an embodiment of the presentapplication.

FIG. 3 is a view schematically showing the structure of an electrode Cwith hybrid single-sided and double-sided coatings according to anembodiment of the present application.

DETAILED DESCRIPTION

Embodiments of the present application will be described in detailbelow. Throughout the specification of the present application, the sameor similar components and components having the same or similarfunctions are denoted by like reference numerals. The embodimentsdescribed herein with respect to the figures are explanatory, andillustrative, and are provided to facilitate the basic understanding ofthe application. The embodiments of the present application should notbe interpreted as limitations to the present application.

Unless otherwise expressly indicated, the following terms used hereinhave the meanings indicated below.

The term “about” is used to describe and illustrate small changes. Whenused in connection with an event or circumstance, the term may refer toan example in which the event or circumstance occurs precisely, and anexample in which the event or circumstance occurs approximately. Forexample, when used in connection with a value, the term may refer to arange of variation less than or equal to ±10% of the said value, such asless than or equal to ±50/%, less than or equal to ±4%, less than orequal to ±3%, less than or equal to ±2%, less than or equal to ±1%, lessthan or equal to ±0.5%, less than or equal to ±0.1%, or less than orequal to ±0.05%. In addition, amounts, ratios, and other values aresometimes presented in a range format in this application. It should beunderstood that such a range format is provided for the sake ofconvenience and simplicity, and should be understood flexibly tocomprise not only the numerical values that are explicitly defined inthe range, but also all the individual values or sub-ranges that arecomprised in the range, as if each value and sub-range are explicitlyspecified.

The term “hydrocarbon group” encompasses alkyl, alkenyl, and alkynylgroups.

The term “alkyl group” is intended to be a linear saturated hydrocarbonstructure having 1 to 20 carbon atoms. The alkyl group is also intendedto be a branched or cyclic hydrocarbon structure having 3 to 20 carbonatoms. When an alkyl group having a specific number of carbon atoms isdefined, it is intended to cover all geometric isomers having saidcarbon number. Therefore, for example, “butyl” refers to n-butyl,sec-butyl, isobutyl, tert-butyl and cyclobutyl; and “propyl” comprisesn-propyl, isopropyl and cyclopropyl. Examples of the alkyl groupcomprise, but are not limited to, methyl, ethyl, n-propyl, isopropyl,cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl,n-pentyl, isoamyl, neopentyl, cyclopentyl, methylcyclopentyl,ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl,cyclopropyl, cyclobutyl, norbornanyl, and the like.

The term “alkenyl group” refers to a monovalent unsaturated hydrocarbongroup which may be straight or branched and which has at least one andusually 1, 2 or 3 carbon-carbon double bonds. Unless otherwise defined,the alkenyl group typically contains from 2 to 20 carbon atoms andcomprises (for example) a —C₂₋₄ alkenyl group, a —C₂₋₆ alkenyl group,and a —C₂₋₁₀ alkenyl group. Representative alkenyl groups comprise (forexample) ethenyl, n-propenyl, iso-propenyl, n-but-2-enyl, butyl-3-enyl,n-hex-3-enyl, and the like.

The term “alkynyl group” refers to a monovalent unsaturated hydrocarbongroup which may be straight or branched and which has at least one andusually 1, 2 or 3 carbon-carbon triple bonds. Unless otherwise defined,the alkynyl group typically contains from 2 to 20 carbon atoms andcomprises (for example) a —C₂₋₄ alkynyl group, a —C₃₋₆ alkynyl group,and a —C₃₋₁₀ alkynyl group. Representative alkynyl groups comprise (forexample) ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl,and the like.

The term “alkylene group” refers to a linear or branched divalentsaturated hydrocarbon group. Unless otherwise defined, the alkylenegroup typically contains from 2 to 10 carbon atoms and comprises (forexample) —C₂₋₃ alkylene and —C₂₋₆ alkylene. The representative alkylenegroup comprises (for example) methylene, ethane-1,2-diyl (“ethylene”),propane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyland the like.

The term “aryl group” refers to a monovalent aromatic hydrocarbon grouphaving a single ring (for example, phenyl) or a fused ring. The fusedring system comprises a completely unsaturated ring system (for example,naphthalene) and a partially unsaturated ring system (for example,1,2,3,4-tetrahydronaphthalene). Unless otherwise defined, the aryl grouptypically contains from 6 to 26 ring carbon atoms and comprises (forexample) a —C₆₋₁₀ aryl group. The representative aryl group comprises(for example) phenyl, methylphenyl, propylphenyl, isopropylphenyl,benzyl and naphthalen-1-yl, naphthalen-2-yl, and the like.

As used herein, the content of each component is based on the totalweight of the electrolyte.

I. Electrolyte

The present application provides an electrolyte, which comprises anelectrolyte and a solvent in which the electrolyte is dissolved. Theelectrolyte of the present application is mainly characterized bycomprising a fluorinated cyclic carbonate and a multi-nitrile compoundhaving an ether bond.

The inventors of the present application found that a composite solidelectrolyte interface film (SEI film) formed of a fluorinated cycliccarbonate and a multi-nitrile compound having an ether bond has lowimpedance and is insusceptible to decomposition during the cycle of thebattery, and thus the interface between the electrolyte and theelectrodes is stable.

The electrolyte of the present application is further mainlycharacterized in that based on the total weight of the electrolyte, theweight percentage (C_(f)) of the fluorinated cyclic carbonate is greaterthan the weight percentage (C_(n)) of the multi-nitrile compound havingan ether bond. When the weight percentages of the fluorinated cycliccarbonate and the multi-nitrile compound having an ether bond conform tothe relationship C_(f)>C_(n), the thickness expansion of the batterycell can be suppressed. When C_(f) and C_(n) satisfy about0.3≤(C_(f)+C_(n))≤about 12 and about 1≤(C_(f)/C_(n))≤about 20, theinhibitory effect is more obvious. When C_(f) and C_(n) satisfy about2≤(C_(f)+C_(n))≤about 8 and about 2≤(C_(f)/C_(n))≤about 10, theinhibitory effect is more particularly obvious.

The electrolyte of the present application plays an important role incontrolling the thickness expansion of the battery cell of theelectrochemical device during repeated charge/discharge cycles. By usingthe electrolyte of the present application, electrochemical devices withexcellent cycle, storage and/or floating-charge performances can beobtained.

1. Multi-Nitrile Compound Having an Ether Bond

In some embodiments, the multi-nitrile compound having an ether bond isselected from a compound represented by General Formula [1]:

where:

R₁, R₂, and R₃ each represent —(CH₂)_(a)—CN or—(CH₂)_(b)—O—(CH₂)_(c)—CN;

R₄ represents hydrogen, an alkyl group having 1-5 carbon atoms,—(CH₂)_(a)—CN, or —(CH₂)_(b)—O—(CH₂)_(c)—CN;

at least one of R₁, R₂, R₃, and R₄ is —(CH₂)_(b)—O—(CH₂)_(c)—CN; and

a, b and c are each independently an integer from 0 to 10.

In some embodiments, the multi-nitrile compound having an ether bondcomprises, but is not limited to, 1,2,3-tris(2-cyanoethoxy)propane,1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane,1,1,1-tris(cyanoethoxymethylene)propane,3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane,1,2,6-tris(cyanoethoxy)hexane, and 1,2,5-tris(cyanoethoxy)pentane. Insome embodiments, the multi-nitrile compound having an ether bondcomprises one or more of those described above.

In some embodiments, the multi-nitrile compound having an ether bondfurther comprises Compound 1A:

In some embodiments, the content C_(n) of the multi-nitrile compoundhaving an ether bond is about 0.1 wt % or more. In some embodiments,C_(n) is about 0.2 wt % or more. In some embodiments, C_(n) is about 0.3wt % or more. In some embodiments, C_(n) is about 0.5 wt % or more. Insome embodiments, C_(n) is about 5 wt % or less. In some embodiments,C_(n) is about 4 wt % or less. In some embodiments, C_(n) is about 3 wt% or less. In some embodiments, C_(n) is about 0.1 wt % to about 5 wt %.

2. Fluorinated Cyclic Carbonate

In some embodiments, the fluorinated cyclic carbonate is selected from afluorinated cyclic carbonate having an alkylene group with 2-6 carbonatoms. In some embodiments, the fluorinated cyclic carbonate comprises,but is not limited to, fluoroethylene carbonate, 4,4-difluoroethylenecarbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylenecarbonate, 4,5-difluoro-4-methylethylene carbonate,4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylenecarbonate, 4-(fluoromethyl)-ethylene carbonate,4-(difluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylenecarbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate,4,5-difluoro-4,5-dimethylethylene carbonate and4,4-difluoro-5,5-dimethylethylene carbonate. In some embodiments, thefluorinated cyclic carbonate comprises one or more of those describedabove.

In some embodiments, the content C_(f) of the fluorinated cycliccarbonate is about 0.1 wt %/o or more. In some embodiments, C_(f) isabout 0.2 wt % or more. In some embodiments, C_(f) is about 0.3 wt % ormore. In some embodiments, C_(f) is about 0.5 wt % or more. In someembodiments, C_(f) is about 10 wt % or less. In some embodiments, C_(f)is about 8 wt % or less. In some embodiments, C_(f) is about 6 wt % orless. In some embodiments, C_(f) is about 0.1 wt % to about 10 wt %.

3. Fluoroether

In some embodiments, the electrolyte of the present application furthercomprises a fluoroether that is selected from compounds of GeneralFormula [2], [3], [4] or [5]:Rf1-O—Rf2  [2],Rf1-O—R  [3],Rf1-O—(R′—O)_(n)—Rf2  [4], andRf1-O—(R′—O)_(n)—R  [5],

or a combination thereof,

where:

in Formulas [2], [3], [4], and [5], Rf1 and Rf2 are each independently alinear or branched C₁ to C₁₂ fluoroalkyl group having at least onehydrogen atom replaced by fluorine, R is a linear or branched C₁ to C₁₂alkyl group, and R′ is a linear or branched C₁ to C₅ alkylene group, andn is an integer from 1 to 5.

In some embodiments, fluoroether comprises, but is not limited to:HCF₂CF₂CH₂OCF₂CF₂H(FEPE), (CF₃)₂CFCF(CF₂CF₃)(OCH₃)(TMMP),CF₃CHFCF₂CH(CH₃)OCF₂CHFCF₃(TPTP), HCF₂CF₂CH₂OCF₂CF₂CF₂CF₂H,HCF₂CF₂OCH₂CF₃, HCF₂CF₂OCH₂CH₂OCF₂CF₂H, HCF₂CF₂OCH₂CH₂CH₂OCF₂CF₂H,HCF₂CF₂CH₂OCF₂CF₂CF₂H, HCF₂CF₂OCH₂CH₂OCF₂CF₂CF₂H,HCF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₂H, CH₃OCH₂CH₂OCH₂CH₂F, CH₃OCH₂CH₂OCH₂CF₃,CH₃OCH₂CH(CH₃)OCH₂CH₂F, CH₃OCH₂CH(CH₃)OCH₂CF₃, FCH₂CH₂OCH₂CH₂OCH₂CH₂F,FCH₂CH₂OCH₂CH(CH₃) OCH₂CH₂F, CF₃CH₂O(CH₂CH₂O)₂CH₂CF₃, andCF₃CH₂OCH₂CH(CH₃)OCH₂CF₃.

The structural formulas of FEPE, TMMP, and TPTP are shown below:

In some embodiments, the fluoroether comprises one or more of thosedescribed above.

In some embodiments, the content of the fluoroether is about 0.01 wt %or more. In some embodiments, the content of the fluoroether is about0.1 wt % or more. In some embodiments, the content of the fluoroether isabout 0.3 wt % or more. In some embodiments, the content of thefluoroether is about 0.5 wt % or more. In some embodiments, the contentof the fluoroether is about 5 wt % or less. In some embodiments, thecontent of the fluoroether is about 4 wt % or less. In some embodiments,the content of the fluoroether is about 3 wt % or less. In someembodiments, the content of the fluoroether is from about 0.01 wt % toabout 5 wt %.

4. Cyclic Phosphonic Anhydride

In some embodiments, the electrolyte of the present application furthercomprises a cyclic phosphonic anhydride, which is selected fromcompounds represented by General Formula [6]:

where:

R₅, R₆, and R₇ are each independently selected from hydrogen, an alkylgroup having 1-20 carbon atoms, or an aryl group having 6-26 carbonatoms.

In some embodiments, R₅, R₆ and R₇ are each independently selected frommethyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl,n-pentyl, iso-pentyl, n-hexyl, iso-hexyl, cyclopentyl,3-methylcyclopentyl, 3-ethylcyclopentyl, cyclohexyl, 4-methylcyclohexyl,4-ethylcyclohexyl, phenyl, benzenemethyl, 4-methylphenyl, 4-propylphenylor 4-iso-propylphenyl.

In some embodiments, R₅, R₆ and R₇ in General Formula [6] are identicalto or different from each other or any two of them are identical.

In some embodiments, the cyclic phosphonic anhydride comprises, but isnot limited to, the following structures:

In some embodiments, the cyclic phosphonic anhydride comprises one ormore of those described above.

In some embodiments, the content of the cyclic phosphonic anhydride isabout 0.01 wt % or more. In some embodiments, the content of the cyclicphosphonic anhydride is about 0.1 wt % or more. In some embodiments, thecontent of the cyclic phosphonic anhydride is about 0.3 wt % or more. Insome embodiments, the content of the cyclic phosphonic anhydride isabout 0.5 wt % or more. In some embodiments, the content of the cyclicphosphonic anhydride is about 3 wt % or less. In some embodiments, thecontent of the cyclic phosphonic anhydride is about 0.01 wt % to about 3wt %.

5. Other Additives

In some embodiments, the electrolyte of the present application furthercomprises at least one of a cyclic carbonate having a carbon-carbondouble bond, a fluorinated chain carbonate, a dinitrile compound, and acompound having a sulfur-oxygen double bond. After the above additivesare added to the electrolyte of the present application, these additivesform, together with the fluorinated cyclic carbonate and themulti-nitrile compound having an ether bond, a strong protective filmwhich is insusceptible to decomposition at the electrode interface ofthe electrochemical device, thereby further suppressing the increase inDC internal resistance of the electrochemical device, reducing thethickness expansion of the battery cell and thus improving thehigh-temperature storage performance and/or the capacity retention rateof the electrochemical device.

(1) Cyclic Carbonate Having a Carbon-Carbon Double Bond

In some embodiments, the cyclic carbonate having a carbon-carbon doublebond comprises, but is not limited to, vinylene carbonate, methylvinylene carbonate, ethyl vinylene carbonate, 1,2-dimethyl vinylenecarbonate, 1,2-diethyl vinylene carbonate, fluorovinylene carbonate, andtrifluoromethylvinylene carbonate; vinyl ethylene carbonate,1-methyl-2-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate,1-n-propyl-2-vinylethylene carbonate, 1-methyl-2-vinylethylenecarbonate, 1,1-divinylethylene carbonate, and 1,2-divinylethylenecarbonate; and 1,1-dimethyl-2-methylene ethylene carbonate, and1,1-diethyl-2-methylene ethylene carbonate. In some embodiments, thecyclic carbonate having a carbon-carbon double bond comprises one ormore of those described above.

In some embodiments, the content of the cyclic carbonate having acarbon-carbon double bond is about 0.01 wt % or more. In someembodiments, the content of the cyclic carbonate having a carbon-carbondouble bond is about 0.1 wt % or more. In some embodiments, the contentof the cyclic carbonate having a carbon-carbon double bond is about 0.3wt % or more. In some embodiments, the content of the cyclic carbonatehaving a carbon-carbon double bond is about 0.5 wt % or more. In someembodiments, the content of the cyclic carbonate having a carbon-carbondouble bond is about 5 wt % or less. In some embodiments, the content ofthe cyclic carbonate having a carbon-carbon double bond is about 3 wt %or less. In some embodiments, the content of the cyclic carbonate havinga carbon-carbon double bond is about 0.01 wt % to about 5 wt %.

(2) Fluorinated Chain Carbonate

In some embodiments, the fluorinated chain carbonate comprises, but isnot limited to, fluoromethylmetyl carbonate, difluoromethylmethylcarbonate, trifluoromethylmethyl carbonate, trifluoroethylmethylcarbonate, and bis(trifluoroethyl) carbonate. In some embodiments, thefluorinated chain carbonate comprises one or more of those describedabove.

In some embodiments, the content of the fluorinated chain carbonate isabout 0.01 wt % or more. In some embodiments, the content of thefluorinated chain carbonate is about 0.1 wt % or more. In someembodiments, the content of the fluorinated chain carbonate is about 0.3wt % or more. In some embodiments, the content of the fluorinated chaincarbonate is about 0.5 wt % or more. In some embodiments, the content ofthe fluorinated chain carbonate is about 5 wt % or less. In someembodiments, the content of the fluorinated chain carbonate is about 3wt % or less. In some embodiments, the content of the fluorinated chaincarbonate is about 1 wt % or less. In some embodiments, the content ofthe fluorinated chain carbonate is about 0.01 wt % to 5 wt %.

(3) Dinitrile Compound

In some embodiments, the dinitrile compound comprises, but is notlimited to, succinonitrile, glutaronitrile, adipodinitrile,1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane,1,8-dicyanooctane, 1,9-dicyanononane, 1,10-dicyanodecane,1,12-dicyanododecane, tetramethylbutanedinitrile,2-methylglutaronitrile, 2,4-dimethylglutaronitrile,2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane,2,5-dimethyl-2,5-hexanedinitrile, 2,6-dicyanoheptane, 2,7-dicyanooctane,2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene,1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,5-dioxa-pimelonitrile,1,4-bis(cyanoethoxy)butane, ethylene glycol bis(2-cyanoethyl)ether,diethylene glycolbis(2-cyanoethyl)ether, triethyleneglycolbis(2-cyanoethyl)ether, tetraethyleneglycolbis(2-cyanoethyl)ether, 3,6,9,12,15,18-hexaoxaeicosanoicdinitrile, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane,1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl)ether,1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene,1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene,1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene,1,6-dicyano-2-methyl-3-hexene, and1,6-dicyano-2-methyl-5-methyl-3-hexene. In some embodiments, thedinitrile compound comprises one or more of those described above.

In some embodiments, the content of the dinitrile compound is about 0.1wt % or more. In some embodiments, the content of the dinitrile compoundis about 0.5 wt % or more. In some embodiments, the content of thedinitrile compound is about 2 wt % or more. In some embodiments, thecontent of the dinitrile compound is about 4 wt % or more. In someembodiments, the content of the dinitrile compound is about 15 wt % orless based on the total weight of the electrolyte. In some embodiments,the content of the dinitrile compound is about 10 wt % or less. In someembodiments, the content of the dinitrile compound is about 8 wt % orless. In some embodiments, the content of the dinitrile compound isabout 0.1 wt % to about 15 wt %.

(4) Compound Having a Sulfur-Oxygen Double Bond

In some embodiments, the compound having a sulfur-oxygen double bondcomprises, but is not limited to, at least one of a cyclic sulfate, achain sulfate, a chain sulfonate, a cyclic sulfonate, a chain sulfite,and a cyclic sulfite.

In some embodiments, the cyclic sulfate comprises, but is not limitedto, 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate,1,2-butylene sulfate, 1,3-butylene sulfate, 1,4-butylene sulfate,1,2-pentylene sulfate, 1,3-pentylene sulfate, 1,4-pentylene sulfate, and1,5-pentylene sulfate. In some embodiments, the cyclic sulfate comprisesone or more of those described above.

In some embodiments, the chain sulfate comprises, but is not limited to,dimethyl sulfate, methyl ethyl sulfate, and diethyl sulfate. In someembodiments, the chain sulfate comprises one or more of those describedabove.

In some embodiments, the chain sulfonate comprises, but is not limitedto, a fluorosulfonate such as methyl fluorosulfonate and ethylfluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyldimesylate, methyl 2-(methylsulfonyloxy)propionate, and ethyl2-(methylsulfonyloxy)propionate. In some embodiments, the chainsulfonate comprises one or more of those described above.

In some embodiments, the cyclic sulfonate comprises, but is not limitedto, 1,3-propanesultone, 1-fluoro-1,3-propanesultone,2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone,1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone,3-methyl-1,3-propanesultone, 1-propene-1,3-sultone,2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone,2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone,1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone,3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone,2-methyl-1-propene-1,3-sultone, 3-methyl-1-propene-1,3-sultone,1-methyl-2-propene-1,3-sultone, 2-methyl-2-propene-1,3-sultone,3-methyl-2-propene-1,3-sultone, 1,4-butane sultone, 1,5-pentane sultone,methylene methanedisulfonate, and ethylene methanedisulfonate. In someembodiments, the cyclic sulfonate comprises one or more of thosedescribed above.

In some embodiments, the chain sulfite comprises, but is not limited to,dimethyl sulfite, methyl ethyl sulfite, and diethyl sulfite. In someembodiments, the chain sulfite comprises one or more of those describedabove.

In some embodiments, the cyclic sulfite comprises, but is not limitedto, 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite,1,2-butylene sulfite, 1,3-butylene sulfite, 1,4-butylene sulfite,1,2-pentylene sulfite, 1,3-pentylene sulfite, 1,4-pentylene sulfite, and1,5-pentylene sulfite. In some embodiments, the cyclic sulfite comprisesone or more of those described above.

In some embodiments, the content of the compound having a sulfur-oxygendouble bond is about 0.01 wt % or more. In some embodiments, the contentof the compound having a sulfur-oxygen double bond is about 0.1 wt % ormore. In some embodiments, the content of the compound having asulfur-oxygen double bond is about 0.3 wt % or more. In someembodiments, the content of the compound having a sulfur-oxygen doublebond is about 0.5 wt % or more. In some embodiments, the content of thecompound having a sulfur-oxygen double bond is about 5 wt % or less. Insome embodiments, the content of the compound having a sulfur-oxygendouble bond is about 4 wt % or less. In some embodiments, the content ofthe compound having a sulfur-oxygen double bond is about 3 wt % or less.In some embodiments, the content of the compound having a sulfur-oxygendouble bond is about 0.01 wt % to about 5 wt % based on the total weightof the electrolyte.

6. Electrolyte

The electrolyte according to the present application is not limited, andmay be any electrolyte known in the art. In some embodiments, theelectrolyte comprises, but is not limited to, an inorganic lithium salt,for example, LiClO₄, LiAsF₆, LiPF₆, LiBF₄, LiSbF₆, LiSO₃F, andLiN(FSO₂)₂ and the like; a fluorine-containing organic lithium salt, forexample, LiCF₃SO₃, LiN(FSO₂)(CF₃SO₂), LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂ cycliclithium 1,3-hexafluoropropane disulfonimide, cyclic lithium1,2-tetrafluoroethane disulfonimide, LiN(CF₃SO₂)(C₄F₉SO₂), LiC(CF₃SO₂)₃,LiPF₄(CF₃)₂, LiPF₄(C₂F₅)₂, LiPF₄(CF₃SO₂)₂, LiPF₄(C₂F₅SO₂)₂, LiBF₂(CF₃)₂,LiBF₂(C₂F₅)₂, LiBF₂(CF₃SO₂)₂, and LiBF₂(C₂F₅SO₂)₂ and the like; and alithium salt containing a dicarboxylic acid complex, for example,lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithiumtris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, andlithium tetrafluoro(oxalato)phosphate and the like. In some embodiments,the electrolyte comprises one or more of those described above. In someembodiments, the electrolyte comprises LiPF₆ and LiBF₄. In someembodiments, the electrolyte comprises a combination of an inorganiclithium salt such as LiPF₆ or LiBF₄ and a fluorine-containing organiclithium salt such as LiCF₃SO₃, LiN(CF₃SO₂)₂, or LiN(C₂F₅SO₂)₂. In someembodiments, the concentration of the electrolyte is in the range ofabout 0.8 mol/L to about 3 mol/L, for example, about 0.8 mol/L to about2.5 mol/L, about 0.8 mol/L to about 2 mol/L, about 1 mol/L to about 2mol/L, for example, 1 mol/L, 1.15 mol/L, 1.2 mol/L, 1.5 mol/L, 2 mol/Lor 2.5 mol/L.

7. Solvent

The solvent used in the electrolyte of the present application may beany non-aqueous solvent known in the art that can be used as a solventfor an electrolyte.

In some embodiments, the non-aqueous solvent comprises, but is notlimited to, a cyclic carbonate, a chain carbonate, a cyclic carboxylate,a chain carboxylate, a cyclic ether, a chain ether, a phosphorus-basedorganic solvent, a sulfur-containing organic solvent, and an aromaticfluorine-containing solvent.

In some embodiments, the cyclic carbonate comprises, but is not limitedto, ethylene carbonate (EC), propylene carbonate (PC), and butylenecarbonate. In some embodiments, the cyclic carbonate has 3-6 carbonatoms.

In some embodiments, the chain carbonate comprises, but is not limitedto, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC),methyl n-propyl carbonate, ethyl n-propyl carbonate, and di-n-propylcarbonate and the like; and a fluorinated chain carbonate, for example,bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate,bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate,bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate,2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate, and2,2,2-trifluoroethylmethyl carbonate.

In some embodiments, the cyclic carboxylate comprises, but is notlimited to, γ-butyrolactone and γ-valerolactone. In some embodiments,some of the hydrogen atoms of the cyclic carboxylate may be substitutedwith fluorine.

In some embodiments, the chain carboxylate comprises, but is not limitedto, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate,butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate,methyl propionate, ethyl propionate, propyl propionate, isopropylpropionate, methyl butyrate, ethyl butyrate, propyl butyrate, methylisobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methylpivalate and ethyl pivalate. In some embodiments, some of the hydrogenatoms of the chain carboxylate may be substituted with fluorine. In someembodiments, the fluorinated chain carboxylate comprises, but is notlimited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyltrifluoroacetate, butyl trifluoroacetate and 2,2,2-trifluoroethyltrifluoroacetate.

In some embodiments, the cyclic ether comprises, but is not limited to,tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane,2-methyl1,3-dioxolane, 4-methyl1,3-dioxolane, 1,3-dioxane, 1,4-dioxaneand dimethoxypropane.

In some embodiments, the chain ether comprises, but is not limited to,dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane,diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane,ethoxymethoxymethane, 1,1-ethoxymethoxyethane and1,2-ethoxymethoxyethane.

In some embodiments, the phosphorus containing organic solventcomprises, but is not limited to, trimethyl phosphate, triethylphosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylenemethyl phosphate, ethylene ethyl phosphate, triphenyl phosphate,trimethyl phosphite, triethyl phosphite, triphenyl phosphite,tris(2,2,2-trifluoroethyl) phosphate andtris(2,2,3,3,3-pentafluoropropyl) phosphate.

In some embodiments, the sulfur-containing organic solvent comprises,but is not limited to, sulfolane, 2-methylsulfolane, 3-methylsulfolane,dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propylsulfone, dimethyl sulfoxide, methyl methanesulfonate, ethylmethanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate,dimethyl sulfate, diethyl sulfate and dibutyl sulfate. In someembodiments, some of the hydrogen atoms of the sulfur-containing organicsolvent may be substituted with fluorine.

In some embodiments, the aromatic fluorine-containing organic solventcomprises, but is not limited to, fluorobenzene, difluorobenzene,trifluorobenzene, tetrafluorobenzene, pentafluorobenzene,hexafluorobenzene and trifluoromethylbenzene.

In some embodiments, the solvent used in the electrolyte of the presentapplication comprises one or more of those described above. In someembodiments, the solvent used in the electrolyte of the presentapplication comprises a cyclic carbonate, a chain carbonate, a cycliccarboxylate, a chain carboxylate and a combination thereof. In someembodiments, the solvent used in the electrolyte of the presentapplication comprises an organic solvent selected from the groupconsisting of ethylene carbonate, propylene carbonate, diethylcarbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethylacetate, and a combination thereof. In some embodiments, the solventused in the electrolyte of the present application comprises ethylenecarbonate, propylene carbonate, diethyl carbonate, ethyl propionate,propyl propionate, γ-butyrolactone, and a combination thereof.

After adding the chain carboxylate and/or the cyclic carboxylate to theelectrolyte of the present application, the chain carboxylate and/or thecyclic carboxylate can form a passivated film on the surface of theelectrode, thereby improving the capacity retention rate after theintermittent charge cycles of the electrochemical device. In someembodiments, the electrolyte of the present application comprises about1 wt % to about 60 wt % of the chain carboxylate, the cycliccarboxylate, or a combination thereof. In some embodiments, theelectrolyte of the present application comprises about 1 wt % to about60 wt %, about 10 wt % to about 60 wt %, about 10 wt % to about 50 wt %,and about 20 wt % to about 50 wt % of ethyl propionate, propylpropionate, γ-butyrolactone or a combination thereof. In someembodiments, the electrolyte of the present application comprises about1 wt % to about 60 wt %, about 10 wt % to about 60 wt %, about 20 wt %to about 50 wt %, about 20 wt % to about 40 wt % or about 30 wt % ofpropyl propionate.

II. Electrochemical Device

The electrochemical device of the present application comprises anydevice in which an electrochemical reaction takes place, and specificexamples comprise all kinds of primary batteries, secondary batteries,fuel cells, solar cells, or capacitors. In particular, theelectrochemical device is a lithium secondary battery including alithium metal secondary battery, a lithium ion secondary battery, alithium polymer secondary battery or a lithium ion polymer secondarybattery. In some embodiments, the electrochemical device of the presentapplication comprises a cathode having a cathode active material capableof absorbing and releasing metal ions; an anode having an anode activematerial capable of absorbing and releasing metal ions; and anelectrolyte of the present application.

1. Electrolyte

The electrolyte used in the lithium ion battery of the presentapplication is any of the electrolytes described above in the presentapplication. Moreover, the electrolyte used in the lithium ion batteryof the present application may comprise other electrolytes fallingwithin the scope of present application.

2. Electrodes

(1) Anode

The anode material used in the electrochemical device of the presentapplication, and the construction and manufacturing methods therefor arenot particularly limited, and may be any of the techniques disclosed inthe prior art. In some embodiments, the anode may be one described inU.S. Pat. No. 9,812,739B, which is incorporated herein by reference inits entirety.

In some embodiments, the anode active material is any substance capableof electrochemically absorbing and releasing a metal ion such as lithiumion. In some embodiments, the anode active material comprises acarbonaceous material, a silicon-carbon material, an alloy material or alithium-containing metal composite oxide material. In some embodiments,the anode active material comprises one or more of those describedabove.

In some embodiments, the anode can be made by any method known in theart. In some embodiments, the anode can be formed by adding a binder anda solvent to the anode active material, and if necessary, adding athickener, a conductive material, a filler, or the like, to prepare aslurry, applying the slurry to a current collector, drying, and thenpressing.

In some embodiments, when the anode comprises an alloy material, ananode active material layer can be formed by vapor deposition,sputtering, or plating.

In some embodiments, when the anode comprises lithium metal, an anodeactive material layer is formed by, for example, a conductive skeletonof a twisted spherical shape and metal particles dispersed in theconductive skeleton, where the conductive skeleton of the twistedspherical shape may have a porosity of about 5% to about 85%, and aprotective layer may be further disposed on the anode active materiallayer of lithium metal.

(2) Cathode

The cathode material used in the electrochemical device of the presentapplication, and the construction and manufacturing methods therefor arenot particularly limited, and may be any of the techniques disclosed inthe prior art. In some embodiments, the cathode may be one described inU.S. Pat. No. 9,812,739B, which is incorporated herein by reference inits entirety.

In some embodiments, the cathode active material comprises, but is notlimited to, a sulfide, a phosphate compound and a lithium-transitionmetal composite oxide. In some embodiments, the cathode active materialcomprises a lithium-transition metal compound which has a structurecapable of deintercalating and intercalating lithium ions.

In some embodiments, the cathode comprises any of the constructionsdisclosed in the prior art. In some embodiments, the cathode has thestructure described in U.S. Pat. No. 9,812,739B.

In some embodiments, the cathode is prepared by forming a cathodematerial with a cathode active material layer including alithium-transition metal compound powder and a binder on a currentcollector.

In some embodiments, the cathode active material layer is generallyproduced by dry mixing a cathode material and a binder (and further aconductive material and a thickener if needed) to form flakes, andpressing the obtained flakes on a cathode current collector; ordissolving or dispersing the material in a liquid medium to form aslurry, coating the slurry on a cathode current collector, and drying.In some embodiments, the cathode active material layer comprises any ofthe materials disclosed in the prior art. In some embodiments, thecathode active material layer comprises materials described in U.S. Pat.No. 9,812,739B.

(3) Electrode Compaction Density

The electrode used in the electrochemical device of the presentapplication comprises a current collector and a coating including asingle-sided coating or a double-sided coating. In some embodiments, asshown by an electrode A in FIG. 1, one side of a current collector 1 iscoated with a slurry to form a coating 2 (that is, the electrodecomprises only a single-sided coating). In some embodiments, as shown byan electrode B in FIG. 2, two opposing sides of a current collector 1are coated with a slurry to form a coating 2 (that is, the electrodecomprises a double-sided coating). In some embodiments, as shown by anelectrode C in FIG. 3, one side of a portion of a current collector 1 iscoated with a slurry to form a coating 2 and the two opposing sides ofthe other portion of the current collector 1 are coated with a slurry toform a coating 2 (that is, the electrode comprises both a single-sidedcoating and a double-sided coating).

In a wound battery, the cathode and the anode are usually each woundfrom an elongated electrode, so that both a single-sided coating and adouble-sided coating are sometimes present on the elongated electrode.In a laminated battery, the cathode and the anode are usually formed bylaminating sheet-like electrodes, and there may be a single-sidedcoating or a double-sided coating on the electrode. In a battery inwhich the wound and laminated electrodes are assembled in combination,the cathode and anode generally each comprise an elongated electrodehaving both a single-sided coating and a double-sided coating, and asheet-like electrode having only a single-sided coating or adouble-sided coating. Generally, both the laminated battery and thewound battery have a single-sided coating and a double-sided coating.

In some embodiments, the electrode has an electrode compaction density.The electrode compaction density is obtained by the following method:determining the thickness of an electrode using a precise measurementtool, such as a ten-thousandths micrometer; then taking the electrode ofan area and accurately measuring the area and weight; and calculatingthe electrode compaction density by a formula below:Electrode compaction density=(Weight of electrode−Weight of currentcollector)/Area of electrode/(Thickness of electrode−Thickness ofcurrent collector)

A lower electrode compaction density makes the porosity higher, causingsome of the particles to be in an insulating state, and be excluded fromcharge and discharge, resulting in a low specific discharge capacity,thus affecting the performance of the electrochemical device. A too highelectrode compaction density may cause difficulty in infiltrability ofthe electrolyte and a decrease in electrolyte retention, such that thecycle and rate performance cannot be guaranteed. Properly controllingthe electrode compaction density of the single-sided and double-sidedcoatings is very important for obtaining electrochemical devices withhigh capacity density, and excellent cycle and storage performance. In ahigh-voltage electrochemical device, the ratio of the electrodecompaction density of the single-sided coating to the electrodecompaction density of the double-sided coating is one of the mainfactors affecting the performance of the electrochemical device. A toohigh or low compaction density ratio will affect the performance of theelectrochemical device.

In some embodiments, the electrode with the single-sided coating has anelectrode compaction density D1, and the electrode with the double-sidedcoating has an electrode compaction density D2, where D1 and D2 satisfythe relationship: about 0.8≤D1/D2≤about 1.2. When D1 and D2 satisfy therelationship, the roles of the cathode and anode active materials arebetter exerted, the thickness expansion of the battery cell iseffectively controlled, and the electrode attains good electricalconductivity. The electrochemical device thus obtained has high capacitydensity and excellent cycle and storage performance.

In some embodiments, D1 and D2 further satisfy the relationship: about0.9≤D1/D2≤about 1.1. In this case, the performance of theelectrochemical device can be further improved.

In some embodiments, D1 and D2 further satisfy the relationship: about0.95≤D1/D2≤about 1.05. In this case, the distribution of pore size andpores in the single-sided coating and the double-sided coating areobviously more uniform, the distribution of the conductive agent and thebinder are also more uniform, such that the contact resistance andcharge exchange resistance of the electrode are lowered, and the activearea participating in the reaction is increased, thereby significantlyimproving the electrochemical performance of the material and furtherimproving the performance of the electrochemical device.

In some embodiments, the electrode may be a cathode or an anode. Whenthe electrode is a cathode, D2 meets the formula: about 3.5g/cm³≤D2≤about 4.3 g/cm³, such that the role of the cathode activematerial is better exerted and the cathode attains good electricalconductivity. When the electrode is an anode, D2 meets the formula:about 1.2 g/cm³≤D2≤about 1.8 g/cm³, such that the anode has a higherbreaking strength, thereby effectively preventing the electrodeparticles from falling off during the cycle.

3. Separator

In some embodiments, the electrochemical device of the presentapplication is provided with a separator between the cathode and theanode to prevent a short circuit. The material and shape of theseparator used in the electrochemical device of the present applicationare not particularly limited, and may use any of the techniquesdisclosed in the prior art. In some embodiments, the separator comprisesa polymer or an inorganic substance or the like formed of a materialwhich is stable against the electrolyte of the present application.

For example, the separator may comprise a substrate layer and a surfacetreatment layer. The substrate layer is a non-woven fabric, film, orcomposite film having a porous structure, and the material of thesubstrate layer is at least one selected from polyethylene,polypropylene, polyethylene terephthalate, and polyimide. Particularly,a porous polypropylene film, a porous polyethylene film, a polypropylenenonwoven fabric, a polyethylene nonwoven fabric, and a porouspolypropylene-polyethylene-polypropylene composite film may be used.

At least one surface of the substrate layer is provided with a surfacetreatment layer, which may be a polymer layer or an inorganic layer, ora layer formed by mixing a polymer and an inorganic material.

The inorganic layer comprises inorganic particles and a binder. Theinorganic particles are at least one selected from alumina, silica,magnesia, titania, hafnium dioxide, tin oxide, cerium dioxide, nickeloxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide,eboehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxideand barium sulfate, or a combination of more than one thereof. Thebinder is one selected from polyvinylidene fluoride, a copolymer ofvinylidene fluoride-hexafluoropropylene, a polyamide, polyacrylonitrile,a polyacrylate ester, polyacrylic acid, a polyacrylate salt,polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate,polytetrafluoroethylene, and polyhexafluoropropylene, or a combinationof more than one thereof.

The polymer layer contains a polymer, and the material of the polymercomprises at least one of a polyamide, polyacrylonitrile, a polyacrylateester, polyacrylic acid, a polyacrylate salt, polyvinylpyrrolidone,polyvinyl ether, polyvinylidene fluoride or poly(vinylidenefluoride-hexafluoropropylene).

III. Application

The electrolyte according to the present application can inhibit theincrease in DC internal resistance of the electrochemical device, sothat the electrochemical device thus manufactured is suitable for use inelectronic devices in various fields.

The use of the electrochemical device of the present application is notparticularly limited and can be used for any purpose known in the art.In an embodiment, the electrochemical device according to the presentapplication is applicable to, but not limited to, notebook computers,pen-input computers, mobile computers, e-book players, portable phones,portable fax machines, portable copiers, portable printers, head-mountedstereo headphones, video recorders, LCD TVs, portable cleaners, portableCD players, mini discs, transceivers, electronic notebooks, calculators,memory cards, portable recorders, radios, backup power sources, motors,vehicles, motorcycles, scooters, bicycles, lighting apparatus, toys,game consoles, clocks, electric tools, flashing light, cameras, largebatteries for household use, and lithium ion capacitors.

EXAMPLES

The performance evaluation of the lithium ion batteries in the examplesand comparative examples of the present application is described below.

1. Preparation of Lithium-Ion Battery

(1) Preparation of Anode

Natural graphite, conductive carbon black (Super-P), styrene-butadienerubber, and sodium carboxymethyl cellulose (CMC) were mixed at a weightratio of 95:2:2:1 in deionized water as a solvent, and stirred untiluniform, to obtain an anode slurry. The anode slurry was coated on acopper foil having a thickness of 12 μm, dried, pressed, and cut, andthen a tab was welded, to obtain an anode.

(2) Preparation of Cathode

Lithium cobaltate (LiCoO₂), conductive carbon black (Super-P) andpolyvinylidene fluoride (PVDF) were mixed at a weight ratio of 95:2:3 inN-methylpyrrolidone (NMP) as a solvent, and stirred until uniform, toobtain a cathode slurry. The cathode slurry was coated on an aluminumfoil having a thickness of 12 μm, dried, pressed, and cut, and then atab was welded, to obtain a cathode.

(3) Preparation of Electrolyte

Under a dry argon atmosphere, to a mixed solvent of EC, PC, and DEC (ata weight ratio of about 1:1:1), then LiPF₆ was added and mixed untiluniform, to form a basic electrolyte, in which the concentration ofLiPF₆ was 1.15 mol/L. The electrolytes were configured according to thefollowing Examples and Comparative Examples.

(4) Preparation of Separator

A porous PE polymer film was used as a separator.

(5) Preparation of Lithium-Ion Battery

The obtained cathode, anode and separator were wound in sequence into alithium ion battery. The lithium ion battery was top-sealed andside-sealed with an aluminum plastic film, with a liquid injection portbeing left. A lithium ion battery was fabricated by injecting theelectrolyte via the liquid injection port, encapsulating, then forming,and capacity grading.

2. Test Method

(1) Test Method for Floating-Charge Performance of Lithium Ion Battery

The lithium ion battery was discharged to 3.0V at 0.5 C, charged to 4.45V at 0.5 C and then to 0.05 C at a constant voltage of 4.45 V at 25° C.,placed in an oven at 50° C., and continuously charged to a cut-offcurrent of 20 mV at a constant voltage of 4.45 V. The thickness changeof the battery cell was monitored. The initial thickness at 50% State ofCharge (SOC) was used as a reference, and an increase in batterythickness of more than 20% was considered a point of failure.

(2) Test Method for High-Temperature Storage Performance of Lithium IonBattery

The lithium ion battery was allowed to stand at 25° C. for 30 minutes,charged to 4.45 V at a constant current of 0.5 C and then to 0.05 C at aconstant voltage of 4.45 V, allowed to stand for 5 minutes, and thenstored at 60° C. for 21 days. The thickness of the battery cell wasmeasured and the thickness expansion rate of the battery cell wascalculated by a formula below:Thickness expansion rate=[(Thickness after storage−Thickness beforestorage)/Thickness before storage]×100%

(3) Test Method for Capacity Retention Rate of Lithium Ion Battery

At 45° C., the lithium ion battery was charged to 4.45 V at a constantcurrent of 1 C and then to a current of 0.05 C at a constant voltage,discharged to 3.0 V at a constant current of 1 C. This was the firstcycle, and multiple cycles were performed on the battery under the aboveconditions. The capacity retention rate of a fresh lithium ion battery(i.e., the lithium ion battery that has completed the aforementionedmanufacturing process and is ready for shipping) and the battery after200 and 400 cycles were calculated separately. The capacity retentionrate after the cycle is calculated according to a formula below:Capacity retention rate after the cycle=(Discharge capacity of acorresponding cycle/Discharge capacity of the first cycle)×100%

(4) Test Method for Voltage Drop of Lithium Ion Battery

At 25° C., the lithium ion battery was charged to 4.45 V at a constantcurrent of 1 C and then to a current of 0.05 C at a constant voltage,discharged to 3.2 V at a constant current of 1 C, and allowed to standfor 5 minutes. Then the voltage was tested, and after 24 hours ofstorage at 85° C., the voltage was tested again. The voltage drop of thelithium-ion battery is calculated according to the formula below:Voltage drop=Voltage before storage−Voltage after storage.

(5) Intermittent Cycle Test Method of Lithium Ion Battery

At 50° C., the lithium ion battery was charged to 4.45 V at a constantvoltage of 0.5 C and then to a cut-off current of 0.05 C at a constantcurrent, allowed to stand for 20 hours, and then discharged to 3.0 V ata constant current of 0.5 C.

Multiple charge/discharge cycles were performed on the battery under theabove conditions. The capacity retention rate of a fresh lithium ionbattery, and the battery after 30, 50, and 100 cycles were calculatedseparately. The capacity retention rate after the cycle is calculatedaccording to a formula below:Capacity retention rate after the cycle=(Discharge capacity of acorresponding cycle/Discharge capacity of the first cycle)×100%

3. Test Results

(1) Effect of the Fluorinated Cyclic Carbonate and the Multi-NitrileCompound Having an Ether Bond on the Performance of the Lithium IonBattery

Table 1 compares the performance of a lithium ion battery (ComparativeExample D1-1) prepared with an electrolyte containing no fluorinatedcyclic carbonate and no multi-nitrile compound having an ether bond, andlithium ion batteries (Examples S1-1 and S1-2) prepared with anelectrolyte comprising a fluorinated cyclic carbonate and amulti-nitrile compound having an ether bond according to the presentapplication.

TABLE 1 Multi-nitrile Thickness Example compound expansion rate Time(hours) of S/Comparative Fluorinated cyclic having an ether afterstorage at floating-charge Example D carbonate (wt %) bond (wt %) 60° C.to failure at 50° C. S1-1 0.2% A1 0.1% B1 6.8% 420 S1-2   2% A1   1% B14.3% 540 D1-1 — — 25.0% 90

As shown in Table 1, Examples S1-1 and S1-2 have significantly reducedthickness expansion rate after storage at 60° C. and/or significantlyincreased time of floating-charge to failure at 50° C. compared withComparative Example D1-1.

Table 2 shows the compositions of the electrolytes used in respectivecomparative examples and examples, and the performance of lithium ionbatteries, in which the content of each component is based on the totalweight of the electrolyte.

TABLE 2 Thickness Time (hours) Example S/ Multi- expansion rate offloating- Comparative Cyclic nitrile after storage at charge to ExampleD carbonate compound 60° C. failure at 50° C. S1-4 4% A1 1% B1 5.5% 519D1-1 — — 25.0% 90 D1-2 4% A1 — 23.4% 160 D1-3 — 1% B1 17.3% 256 D1-4 1%VC 1% SN 21.4% 178 D1-5 4% A1 1% SN 13.7% 367 D1-6 1% VC 1% EDN 16.5%216 D1-7 1% VC 1% B1 15.6% 318 D1-8 4% VC 1% B1 23.7% 320

As shown in Table 2, the electrolytes of Example S1-4 contain thefluorinated cyclic carbonate A1 and the multi-nitrile compound having anether bond B1. The electrolyte of Comparative Example D1-1 does notcontain a fluorinated cyclic carbonate and a multi-nitrile compoundhaving an ether bond. The electrolyte of Comparative Example D1-2 merelycontains the fluorinated cyclic carbonate (A1). The electrolyte ofComparative Example D1-3 merely contains the multi-nitrile compoundhaving an ether bond (B1). The electrolyte of Comparative Example D1-4contains the non-fluorinated cyclic carbonate (VC) and the multi-nitrilecompound having no ether bond (SN). The electrolyte of ComparativeExample D1-5 contains the fluorinated cyclic carbonate (A1) and themulti-nitrile compound having no ether bond (SN). The electrolytes ofComparative Examples D1-6, D1-7, and D1-8 contain the non-fluorinatedcyclic carbonate (VC) and the multi-nitrile compound having an etherbond (EDN or B1).

The results show that the lithium ion battery (Example S1-4) preparedwith an electrolyte containing a fluorinated cyclic carbonate and amulti-nitrile compound having an ether bond according to the presentapplication has a significantly lower thickness expansion rate afterstorage at 60° C. and/or a significantly higher time of floating-chargeto failure at 50° C. than the lithium ion batteries (ComparativeExamples D1-1 to D1-8) prepared with an electrolyte containing nofluorinated cyclic carbonate and or no multi-nitrile compound having anether bond. That is, the lithium ion battery produced with theelectrolyte of the present application has more excellent storage and/orfloating-charge performance.

(2) Effect of the Weight Percentage (C_(f)) of the Fluorinated CyclicCarbonate and the Weight Percentage (C_(n)) of the Multi-NitrileCompound Having an Ether Bond on the Performance of Lithium IonBatteries

Table 3 shows the compositions of the electrolytes used in respectivecomparative examples and examples, and the storage and floating-chargingperformance of lithium ion batteries.

TABLE 3 Thickness Time (hours) Multi-nitrile expansion of floating-Example S/ Fluorinated compound rate charge Comparative cyclic having anafter storage to failure at Example D carbonate ether bond at 60° C. 50°C. S1-1 0.2% A1   0.1% B1   6.8% 420 S1-2 2% A1 1% B1 4.3% 540 S1-3 3%A1 1% B1 5.4% 520 S1-4 4% A1 1% B1 5.5% 519 S1-5 5% A1 1% B1 5.8% 521S1-6 6% A1 1% B1 6.3% 517 S1-7 10% A1  0.5% B1   7.5% 480 S1-8 5% A1 2%B1 4.8% 620 S1-9 4% A1 2% B1 4.1% 780 S1-10 4% A2 2% B2 4.3% 660 S1-114% A2 0.5% B2   5.8% 490 S1-12 4% A2 0.2% B2   6.3% 469 S1-13 4% A3 2%B3 4.4% 580 S1-14 2% A3 1% B3 5.3% 520 S1-15 2% A4 1% B4 5.4% 510 S1-162% A1 1% Compound 4.1% 598 1A S1-17 2% A2 1% Compound 4.3% 591 1A S1-1811% A1  2% B1 8.5% 489 S1-19 10% A1  5% B1 8.8% 450 S1-20 10% A1  0.4%B1   9.1% 467 S1-21 10% A1  0.2% B1   10.6% 435 D1-9 1% A1 5% B1 12.1%340

As shown in Table 3, C_(f) is less than C_(n) in the electrolyte used inComparative Example D1-9. The results of Examples S1-1 to S1-21 in Table3 indicate that compared with Comparative Example D1-9, when C_(f) andC_(n) in the electrolyte were adjusted to satisfy C_(f)>C_(n), thelithium ion battery prepared with the electrolyte of the presentapplication has a lower thickness expansion rate after storage at 60° C.and/or a higher time of floating-charge to failure at 50° C. Comparedwith Examples S1-18 and S1-19, when C_(f) and C_(n) satisfy about 0.3 wt%≤(C_(f)+C_(n))≤about 12 wt %, the lithium ion battery prepared with theelectrolyte of the present application has a significantly lowerthickness expansion rate after storage at 60° C. and/or a significantlyhigher time of floating-charge to failure at 50° C. Compared withExamples S1-20 and S1-21, when C_(f) and C_(n) satisfy about1≤(C_(f)+C_(n))≤about 20, the lithium ion battery prepared with theelectrolyte of the present application has a significantly lowerthickness expansion rate after storage at 60° C. and/or a significantlyhigher time of floating-charge to failure at 50° C. When C_(f) and C_(n)satisfy about 2 wt %≤(C_(f)+C_(n))≤about 8 wt % and/or about2≤(C_(f)/C_(n))≤about 10, the fluorinated cyclic carbonate andmulti-nitrile compound having an ether bond exhibit an synergisticeffect, and the lithium ion battery prepared therewith has exceptionallyexcellent high temperature storage and/or floating-charge performance.The above results show that the lithium ion battery produced with theelectrolyte of the present application has excellent storage and/orfloating-charge performance over the prior art.

(3) Effect of Fluoroether on the Performance of the Lithium Ion Battery

Table 4 shows the performance of lithium ion batteries prepared byadding different weight percentages of fluoroether to an electrolytecontaining 4 wt % fluorinated cyclic carbonate (A1) and 1 wt %multi-nitrile compound having an ether bond (B1).

TABLE 4 Example S/ DC internal resistance 21-day thickness Comparative(mohm) of fresh expansion rate Example D Fluoroether battery at 20% SOCat 60° C. S1-4 — 62.1 8.3% S2-1 0.1% D1   49.2 5.6% S2-2 0.5% D1   48.85.3% S2-3 1% D1 47.6 4.8% S2-4 2% D1 47.4 4.3% S2-5 3% D1 47.7 4.3% S2-64% D1 48.2 4.4% S2-7 5% D1 49.3 4.5% S2-8 1% D2 49.2 4.7% S2-9 1% D348.4 4.5% D2-1 6% D1 50.3 7.6%

As shown by Examples S2-1 to S2-7, as the content of the fluoroether isincreased from 0.1 wt % to 5 wt %, the DC internal resistance at 20% SOCand the 21-day thickness expansion rate at 60° C. of the fresh lithiumion battery are further reduced. When the fluoroether content is greaterthan 5 wt %, the DC internal resistance and the storage performance areslightly deteriorated.

(4) Effect of Cyclic Phosphonic Anhydride on the Performance of theLithium Ion Battery

Table 5 shows the performance of lithium ion batteries prepared byadding different weight percentages of cyclic phosphonic anhydride to anelectrolyte containing 4 wt % fluorinated cyclic carbonate A1 and 1 wt %multi-nitrile compound having an ether bond (B1).

TABLE 5 Changes of DC internal Example S/ Cyclic resistance at 20% SOCCapacity retention rate Comparative phosphonic Fresh After After FreshAfter After Example D anhydride battery 200 cycles 400 cycles battery200 cycles 400 cycles S1-4 — 62.1 78.3 112.5 100% 90.1% 82.1% S3-1 0.1%E1  47.3 51.5 88.2 100% 95.7% 90.1% S3-2 0.5% E1  45.4 47.2 81.3 100%96.2% 91.3% S3-3 1% E1 43.6 47.1 80.5 100% 96.1% 90.7% S3-4 2% E1 44.646.3 81.6 100% 95.1% 89.6% S3-5 3% E1 44.9 49.1 88.4 100% 94.7% 88.4%S3-6 1% E2 44.2 48.3 87.3 100% 95.2% 90.9% S3-7 1% E3 45.3 47.7 88.5100% 95.1% 90.7% D3-1 4% E1 46.1 58.6 104.3 100% 92.0% 85.3%

The results show that the addition of cyclic phosphonic anhydride to theelectrolyte of the present application can reduce the DC internalresistance of the lithium ion battery before and after the cycle, andimprove the storage performance of the lithium ion battery. As shown byExamples S3-1 to S3-7, as the content of cyclic phosphonic anhydrideincreases from 0.1 wt % to 3 wt %, the DC internal resistance at 20% SOCof the lithium ion battery decreases first and then rises, and thecapacity retention rate of the lithium ion battery increases first andthen decreases. When the content of cyclic phosphonic anhydride isgreater than 3 wt %, the cycle performance is affected, possibly due tothe decomposition of the cyclic phosphonic anhydride.

(5) Effect of Fluoroether and Cyclic Phosphonic Anhydride in Combinationon the Performance of the Lithium Ion Battery

Table 6 shows the performance of lithium ion batteries prepared byadding different weight percentages of fluoroether and cyclic phosphonicanhydride to an electrolyte containing 4 wt % fluorinated cycliccarbonate (A1) and 1 wt % multi-nitrile compound having an ether bond(B1).

TABLE 6 21-day Changes of DC internal thickness Cyclic resistance at 20%SOC expansion Capacity retention rate Example Fluoroether phosphonicFresh After After rate at Fresh After After S D1 anhydride E1 battery200 cycles 400 cycles 60° C. battery 200 cycles 400 cycles S1-4 — — 62.178.3 112.5 8.3% 100% 90.1% 82.1% S2-3 1% — 48.8 55.2 89.7 5.3% 100%92.3% 85.8% S3-3 —  1% 43.6 47.1 80.5 5.1% 100% 96.1% 90.7% S4-1 0.1% 0.5% 44.6 48.7 80.5 5.7% 100% 94.3% 89.9% S4-2 1% 0.5% 43.3 45.4 80.25.0% 100% 95.3% 90.2% S4-3 1% 0.3% 43.8 47.5 78.9 4.0% 100% 95.8% 90.5%S4-4 1% 0.1% 46.1 50.4 85.5 4.2% 100% 94.7% 90.7% S4-5 3%  2% 42.6 4780.7 3.7% 100% 94.1% 89.2%

The results show that the addition of fluoroether and cyclic phosphonicanhydride to the electrolyte of the present application can furtherreduce the DC internal resistance of the lithium ion battery before andafter the cycle, and improve the storage performance of the lithium ionbattery.

(6) Effect of Other Additives on the Performance of the Lithium IonBattery

Table 7 shows the performance of lithium ion batteries prepared byadding different weight percentages of other additives to an electrolytecontaining 4 wt % fluorinated cyclic carbonate (A1) and 1 wt %multi-nitrile compound having an ether bond (B1).

TABLE 7 Voltage drop (V) after storage at Example S/ 3.2 V andComparative 85° C. for Example D VC VEC PS DTD Dinitrile 24 hours S1-4 —— — — — 0.37 S5-1 0.5% — — — — 0.32 S5-2 0.5% — 3% — — 0.29 S5-3 0.5% —3% 0.5% — 0.2 S5-4  1% — 3% — — 0.27 S5-5  1% — 3% 0.5% — 0.17 S5-6 —0.5% 3% 0.5% — 0.22 S5-7 — — 3% — — 0.31 S5-8 — — — 0.5% — 0.25 S5-90.5% — 3% — 2% SN  0.15 S5-10 — — — —  2% ADN 0.3 S5-11 — — 3% — 2% EDN0.21

The results show that the addition of film-forming additives such as VC,VEC, PS, SN, ADN, DTD and EDN to the electrolyte of the presentapplication can further improve the SEI stability of the lithium ionbattery and suppress the voltage drop of the lithium ion battery. Thecombined use of various additives is beneficial to the furtherimprovement of the stability of the lithium ion battery, facilitates thelong-term storage of the lithium ion battery, and improves thereliability of the lithium ion battery.

(7) Effect of Carboxylate on the Performance of the Lithium Ion Battery

Table 8 shows the performance of lithium ion batteries prepared byadding different weight percentages of carboxylate to an electrolytecontaining 4 wt %/o fluorinated cyclic carbonate (A1) and 1 wt %multi-nitrile compound having an ether bond (B1).

TABLE 8 Capacity retention rate after intermittent cycle After 30 After50 After 100 Example S Carboxylate Fresh battery cycles cycles cyclesS1-4 0 100% 73.3% 64.0% 53.9% S6-1  1% H1 100% 81.7% 73.8% 63.9% S6-210% H1 100% 83.5% 78.7% 76.2% S6-3 20% H1 100% 85.7% 80.5% 77.8% S6-430% H1 100% 87.4% 82.6% 78.9% S6-5 40% H1 100% 86.5% 79.7% 74.9% S6-650% H1 100% 84.6% 77.4% 72.1% S6-7 60% H1 100% 82.3% 75.8% 70.5% S6-810% H2 100% 81.6% 75.4% 72.4% S6-9 20% H2 100% 85.3% 80.1% 77.2% S6-1030% H2 100% 87.3% 82.1% 78.2% S6-11 40% H2 100% 86.2% 79.1% 74.4% S6-1250% H2 100% 83.6% 75.6% 71.2% S6-13 60% H2 100% 81.5% 74.6% 69.9% S6-1410% H3 100% 81.9% 75.1% 71.6%

As shown by Examples S6-1 to S6-13, as the carboxylate contentincreases, the capacity retention rate after the intermittent cycle ofthe lithium ion battery is increased. When the carboxylate content isclose to 60 wt %, the intermittent cycle performance of the lithium ionbattery is affected, mainly due to the side reactions between LiPF₆ andthe carboxylate. Therefore, when a carboxylate is used, the contentthereof needs to be adjusted properly.

(8) Effect of Electrode Compaction Density on the Performance of theLithium Ion Battery

Table 9 shows the performance at various compaction ratios (D1/D2) oflithium ion batteries prepared with an electrolyte containing 4 wt %fluorinated cyclic carbonate (A1), 1 wt % multi-nitrile compound havingan ether bond (B1) and 30 wt % propyl propionate.

Example Compaction Capacity retention rate S/Comparative density ratioFresh After 200 After 400 Example D (D1/D2) battery cycles cycles S7-10.8 100% 93.4% 88.8% S7-2 0.9 100% 95.0% 89.9% S7-3 0.95 100% 95.9%90.7% S7-4 1 100% 96.8% 91.2% S7-5 1.05 100% 95.8% 90.6% S7-6 1.1 100%94.9% 89.9% S7-7 1.2 100% 93.5% 88.6% D7-1 1.3 100% 90.7% 83.4% D7-2 0.7100% 90.3% 82.5%

The results show that the electrode compaction density ratio of thelithium ion battery (electrode compaction density D1 of single-sidedcoating/electrode compaction density D2 of double-sided coating) has asignificant effect on the cycle performance of the lithium ion battery.A too large or too small D1/D2 will damage the cycle performance of thelithium-ion battery. When D1/D2 is between about 0.8 and about 1.2, thelithium ion battery attains an excellent performance (as shown byExamples S7-1 to S7-7). When D1/D2 is between about 0.9 and about 1.1,the lithium ion battery attains an exceptionally excellent performance(as shown by Examples S7-2 to S7-6). When D1/D2 is greater than about1.2 or less than about 0.8, the performance of the lithium ion batteryis poor (as shown by Comparative Examples D7-1 and D7-2).

Table 10 shows the performance at various compaction density ratiosD1/D2 of lithium ion batteries prepared by adding different weightpercentages of fluoroether and/or cyclic phosphonic anhydride to anelectrolyte containing 4 wt % fluorinated cyclic carbonate (A1) and 1 wt% multi-nitrile compound having an ether bond (B1).

TABLE 10 Cyclic Compaction Capacity retention rate Example Fluoroetherphosphonic density Fresh After After S D1 anhydride E1 ratio (D1/D2)battery 200 cycles 400 cycles S8-1 1% — 0.8 100% 94.9% 89.7% S8-2 1% — 1100% 97.1% 91.8% S8-3 1% — 1.2 100% 94.3% 89.6% S8-4 — 0.3% 0.8 100%93.9% 89.2% S8-5 — 0.3% 1 100% 97.6% 92.2% S8-6 — 0.3% 1.2 100% 93.7%89.1% S8-7 1% 0.3% 1 100% 98.1% 93.1%

The results show that the lithium ion battery achieves a furtherimproved cycle performance when the compaction density ratio (D1/D2) isbetween about 0.8 and about 1.2 after the addition of fluoroether and/orcyclic phosphonic anhydride to the electrolyte of the presentapplication.

References throughout the specification to “some embodiments”, “partialembodiments”, “one embodiment”, “another example”, “example”, “specificexample” or “partial examples” mean that at least one embodiment orexample of the application comprises specific features, structures,materials or characteristics described in the embodiments or examples.Thus, the descriptions appear throughout the specification, such as “insome embodiments”, “in an embodiment”, “in one embodiment”, “in anotherexample”, “in an example”, “in a particular example” or “for example”,are not necessarily the same embodiment or example in the application.Furthermore, the particular features, structures, materials orcharacteristics herein may be combined in any suitable manner in one ormore embodiments or examples.

While the illustrative embodiments have been shown and described, itwill be understood by those skilled in the art that the embodiments arenot to be construed as limiting the present application, andmodifications, substitutions and changes can be made to the embodimentswithout departing from the spirit and scope of the present application.

The above-described embodiments of the present application are intendedto be illustrative only. Numerous alternative embodiments may be devisedby persons skilled in the art without departing from the scope of thefollowing claims.

ABBREVIATION

Abbreviation Material Name A1 Fluoroethylene carbonate A24,4-difluoroethylene carbonate A3 4,5-difluoroethylene carbonate A44-fluoro-5-methylethylene carbonate ADN Adiponitrile B11,2,3-tris(2-cyanoethoxy)propane B2 1,2,4-tris(2-cyanoethoxy)butane B31,2,6-tris(cyanoethoxy)hexane B4 1,2,5-tris(cyanoethoxy)pentane D11,1-difluoro-2,2-difluoroethyl-2′,2′-difluoro-3′,3′- difluoropropylether (FEPE) D2 2-trifluoromethyl-3-methoxyperfluoropentane (TMMP) D32-(trifluoro-2-fluoro-3-difluoropropoxy)-3-difluoro-4-fluoro-5-trifluoropentane (TPTP) DTD 1,2-ethylene sulfate E1 Cyclictripropyl phosphonic anhydride (T3P) E2 Cyclic trimethyl phosphonicanhydride (TM3P) E3 Cyclic triethyl phosphonic anhydride (TE3P) EDNEthylene glycol bis(2-cyanoethyl) ether H1 Propyl propionate H2 Ethylpropionate H3 γ-butyrolactone PS 1,3-propanesultone SN Succinonitrile VCVinylene carbonate VEC Vinyl ethylene carbonate

What is claimed is:
 1. An electrolyte, comprising a fluorinated cycliccarbonate, a multi-nitrile compound having an ether bond, and adinitrile compound; wherein the dinitrile compound comprises at leastone selected from the group consisting of succinonitrile andadiponitrile; based on the total weight of the electrolyte, the weightpercentage (C_(f)) of the fluorinated cyclic carbonate is greater thanthe weight percentage (C_(n)) of the multi-nitrile compound having theether bond, wherein based on the total weight of the electrolyte, C_(f)is about 0.1 wt %-about 10 wt %, and C_(n) is about 0.1 wt %-about 5 wt%, and wherein the multi-nitrile compound having an ether bond isselected from at least one of the group consisting of1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane,1,1,1-tris(cyanoethoxymethylene)ethane,1,1,1-tris(cyanoethoxymethylene)propane,3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane,1,2,6-tris(cyanoethoxy)hexane, and 1,2,5-tris(cyanoethoxy)pentane. 2.The electrolyte according to claim 1, wherein the multi-nitrile compoundhaving an ether bond comprises Compound 1A:


3. The electrolyte according to claim 1, wherein the fluorinated cycliccarbonate is selected from a fluorinated cyclic carbonate having analkylene group with 2-6 carbon atoms.
 4. The electrolyte according toclaim 1, wherein the fluorinated cyclic carbonate is selected from atleast one of the group consisting of fluoroethylene carbonate,4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate,4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylenecarbonate, 4-fluoro-5-methylethylene carbonate,4,4-difluoro-5-methylethylene carbonate, 4-(fluoromethyl)-ethylenecarbonate, 4-(difluoromethyl)-ethylene carbonate,4-(trifluoromethyl)-ethylene carbonate,4-(fluoromethyl)-4-fluoroethylene carbonate,4-(fluoromethyl)-5-fluoroethylene carbonate,4-fluoro-4,5-dimethylethylene carbonate,4,5-difluoro-4,5-dimethylethylene carbonate, and4,4-difluoro-5,5-dimethylethylene carbonate.
 5. The electrolyteaccording to claim 1, wherein the electrolyte further comprises afluoroether selected from compounds represented by General Formula [2],[3], [4] or [5]:Rf1-O—Rf2  [2],Rf1-O—R  [3],Rf1-O—(R′—O)_(n)—Rf2  [4],Rf1-O—(R′—O)_(n)—R  [5], or a combination thereof, where: in Formulas[2], [3], [4], and [5], Rf1 and Rf2 are each independently a linear orbranched C₁ to C₁₂ fluoroalkyl group having at least one hydrogen atomreplaced by fluorine, R is a linear or branched C₁ to C₁₂ alkyl group,and R′ is a linear or branched C₁ to C₅ alkylene group, and n is aninteger from 1 to
 5. 6. The electrolyte according to claim 1, whereinthe electrolyte further comprises a cyclic phosphonic anhydride selectedfrom compounds represented by General Formula [6]:

where: R₅, R₆, and R₇ are each independently selected from hydrogen, analkyl group having 1-20 carbon atoms, or an aryl group having 6-26carbon atoms, and R₅, R₆ and R₇ are identical to or different from eachother or any two of them are identical.
 7. The electrolyte according toclaim 1, wherein the electrolyte further comprises at least one of acyclic carbonate having a carbon-carbon double bond, a fluorinated chaincarbonate, and a compound having a sulfur-oxygen double bond.
 8. Theelectrolyte according to claim 1, wherein the electrolyte furthercomprises at least one of a cyclic carbonate, a chain carbonate, acyclic carboxylate, a chain carboxylate, a cyclic ether, a chain ether,a phosphorus-based organic solvent, a sulfur-containing organic solvent,and an aromatic fluorine-containing solvent.